ROCKPORT – A survey of lobster larvae suggests that landings may fall off this year and next.

And the dreaded lobster shell disease, which devastated the fishery in Long Island Sound in 1997 and is beginning to be seen in Maine, may be linked to decaying plastics in the environment.

Or maybe not.

There is no shortage of scientists working to understand what makes lobsters tick, but studying the creatures seems to leave the researchers with as many questions as answers.

Several top researchers shared data Friday at a session of the Maine Fishermen’s Forum at the Samoset Resort.

Lewis Incze, a senior research scientist at the University of Southern Maine’s Bioscience Research Institute, gave an update on surveys of lobster larvae. The ongoing study follows the larvae from a point off Grand Manan Island, near the U.S.-Canada border, as they drift south and west along the Maine coast.

The number of larvae “was down for a period of years” several years ago, Incze said, but forecasting what that means for the adult lobster population is tricky.

“We don’t exactly know how fast lobsters are growing,” he said. “The jury is still out.”

But Incze said his projections show that the number of legal-size lobsters could begin declining this year, and might continue for a year or two. At the same time, he said, the decline should have been noticed last year, and was not.

Research by the Penobscot Bay Marine Resources Collaborative, reported in December 2000, forecast lower lobster landings in 2004 and 2005.

Jim Manning of the New England Fisheries Science Center showed how specially designed floating devices – plastic pipe attached to buoys, which he called “drifters” – validated the existing understanding of how the current carries larval and juvenile lobster from east to west.

The devices, some equipped with Global Positioning System technology, were dropped off Isle au Haut and floated along the coast as far as Cape Cod. Some circulated around and returned to Isle au Haut.

Other drifters, dropped nearer to the coast, often ended up in local bays and rivers, Manning said, suggesting that some juvenile lobster fall through the water column to the bottom and mature near shore.

A fisherman from Nova Scotia said he and others often find Maine lobster buoys in Canadian waters, suggesting that the floating gear circulates counterclockwise in the Gulf of Maine.

Kathy Castro of the University of Rhode Island has been studying lobster shell disease in the aftermath of the demise of lobsters in Long Island Sound in 1997.

“When Long Island Sound collapsed, Rhode Island took a good, hard look” at the disease, she said.

While little is known about its cause, the disease – which leaves the crustaceans’ shells scoured rough, thin and blackened – has been documented off Buzzards Bay in 1998; in the Hudson Canyon, off the south shore of Long Island and off Boston in 2000; and in Maine in recent years.

In Maine, just one-tenth of 1 percent of the catch is affected, said Carl Wilson of the state Department of Marine Resources.

In Rhode Island, the problem is worse.

“More than 30 percent of our catch has shell disease,” Castro said. “We’re starting to see this major spread-out from where it started.”

When lobsters are obviously afflicted, she said, fishermen cannot get the same price for them at market.

“There’s a huge economic impact,” Castro said.

A study released last month suggests that affected lobsters have absorbed a manmade agent that comes from plastics and epoxies. The compound mimics a lobster hormone, she said, and may disrupt shell production.

Castro said the big question is: “Why now?”

In her sampling in Rhode Island waters, she found that 60 percent of egg-bearing female lobsters have the disease. That might be because those lobsters keep their shells longer.

At this point in the research, there is a lot of cause-and-effect speculation. Castro said the behavior of affected lobsters changes, as they are observed spending more time in shelter and eating less.

“There seems to be some kind of hormonal imbalance in these lobsters,” she said.

Wilson said DMR has posted bulletins near docks along the coast, and fishermen have responded with reports of afflicted lobsters from Kittery to Eastport.

The impact on the creatures seems less severe than in southern New England lobsters, he said.